In the fields of medical diagnosis and graphic arts, there have been concerns in processing of photographic film with respect to effluent produced from wet-processing of image forming materials, and recently, reduction of the processing effluent has been strongly demanded in terms of environmental protection and space saving. Accordingly, there has been desired techniques relating to a photothermographic material in which efficient light-exposure is feasible as is done in a laser imager or laser image setter and by which definite, clear black images are obtained. There have been known a silver salt photothermographic dry imaging material comprising on a support an organic silver salt, light-sensitive silver halide and a reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. H. Klosterboer, “Dry Silver Photographic Materials” (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991). This silver salt photothermographic dry imaging material (hereinafter, also denoted simply as photothermographic material) advantageously renders possible formation of distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter. Thus, in the light-sensitive layer of the photothermographic material, light-sensitive silver halide and organic silver salt function as a photosensor and silver source, respectively, which are thermally developed at a temperature of 80 to 250° C. with the reducing agent to form images, without being further subjected to fixing.
The foregoing photothermographic material, after exposure, is processed by thermal developing at a temperature of from 80 to 250° C. without fixing, so that at least a part of silver halide, an organic silver salt or a reducing agent remains after thermal development, resulting in formation of metallic silver due to heat or light after storage over a long period of time and arising in problems that image quality such as silver image tone changes easily. There have been employed halogen compounds capable of oxidizing silver through photoinduction as a technique for preventing variation or deterioration of silver images and specific examples of such halogen compounds are disclosed, for example, in JP-A Nos. 7-2781, 6-208193 and 50120328 (hereinafter, the term, JP-A refers to an unexamined Japanese Patent Application Publication). However, the disclosed compounds, in general, have a tendency of displaying an oxidizing function upon thermal decomposition, and they are effective in preventing formation of fog or growth thereof, while it was also proved that there are problems that they inhibited silver image formation, leading to disadvantages such as reduction of sensitivity, maximum density and silver covering power. To overcome such problems, there is known the use of dyes capable of absorbing exposed light, so-called antihalation dyes. An antihalation dye, which is most effectively incorporated between a photosensitive layer and a support, exhibits interlayer diffusibility and is difficult to be fixed into an intended layer so that when photosensitive layer are simultaneously or successively coated, the dye diffuses into the photosensitive layers, resulting in competition for incident light with silver halide and leading to reduced sensitivity. In cases where a layer containing a pigment capable of absorbing exposed light is provided between a photosensitive layer and a support, color remained after thermal development becomes a problem. In light of the foregoing, specifically when coating a coating solution containing an organic solvent, there has been desired a technique of stably fixing a dye into a specific layer, specifically between the photosensitive layer and the support.
To overcome the foregoing problems, there is disclosed a technique of using dyes soluble in organic solvent with the intent of preventing halation caused by laser light, as disclosed in JP-A Nos. 8-201959 and 2001-83655. However, it is the present status that it is difficult to say that such a technique has overcome the foregoing problems.
To attain fixation, various techniques for micro-capsulation of dyes have been in the art. However, in the status, it is difficult to synthesize a microcapsule having a diameter capable of being stably incorporated into an intended layer and being coated, or to stably hold a dye contained in a core in an organic solvent.